Microparticles are used in a wide variety of applications and substances, including as stationary phases for chromatography, as catalyst supports, as additives for improving the mechanical properties of polymers, as substrates in biological assays, and as pigments in paints. For many such applications the particles include coatings for providing desired chemical functionality or physical properties to the particle surface, and/or protecting the particle substrate from outside reagents. As an example, hydrocarbon-coated silica microparticles are used in reverse-phase chromatography to separate substances of interest according to their affinity for the particles.
It is often desirable to ensure that the coating is robustly attached to the particle substrate. For example, in chromatography applications, it is desirable that the coating attachment be chemically insensitive to the eluted reagents. In microparticle/polymer composites, robust coating attachments can ensure the preservation of desired adhesion of the microparticles to the polymers. Covalent bonding of the coating to the substrate generally allows a more robust coating attachment than other bonding mechanisms such as surface adsorption or ionic bonding.
Covalently bonding a coating to a surface can be performed by reacting particles of the substrate material with various coating agents. Such reactions may require the use of specialized compounds and processes, and may not yield chemically robust bonds. In addition, such reactions may make the manufacturing process relatively expensive and/or incompatible with functional groups desired on the particle surface. For example, reverse phase silica gel particles can be generated by coating fine, clean sand (silica gel) with a hydrocarbon layer. The coating process may require the use of multiple reagents and reaction steps for attaching the hydrocarbon layer to the silica gel. In addition, some covalent coating attachments (e.g. through silicon-oxygen-silicon bonds) can be relatively sensitive to hydrolysis or other chemical reactions.